Epitope tagging is a widely accepted technique that fuses an epitope peptide to a certain protein as a marker for gene expression. With this technique, gene expression can be easily monitored on Western blotting, immunoprecipitation and immunofluorescence utilizing an antibody that recognizes such an epitope. The Ha-Tag (YPYDVPDYA) corresponds to the partial peptide sequence of the influenza hemagglutinin protein.

Immunoprecipitation analysis of HA tagged I -kB protein from transfectant with HA-tag pAb ; immunocomplex was resolved on SDS-PAGE after immunoprecipitation with the antibody, and immunoblotted with HA -tag pAb.